Content is generally delivered to computers over the internet (and using Web technologies) under the HTTP specification, which defines the format for requests for data and responses to those requests. Under that specification, the GET method is used to request data from a specified resource, while the POST method submits to a specified resource data that is to be processed. A server system may respond to such methods by transmitting content, such as web page content (using, e.g., HTML, JavaScript, and the like) to the requesting computer (e.g., desktop, laptop, smartphone, watch, or tablet).
Certain requests may be made frequently and may result in the same content being served. Such repeated requests can place a load on an originating server system and on the network, and can also lead to latency in the operation of the requesting computer. As a result, information can be cached to address some of these issues. For example, a server system can cache information that does not change and may perform “expensive” operations on it only periodically, and instead serve a more static version of the information. Also, components in the network (e.g., at large internet service providers) can save copies of some web pages, serve those cached copies across multiple requests, and only periodically obtain up-to-date copies from the original server system. And at the client, information can also be cached—e.g., if a user moves quickly to a page and then arrows back to a prior page, a browser might not fetch the prior page, but may instead rely on a version of the page that was acquired before the user moved to the second page.